This invention generally relates to an improved process for preparing squaraine compositions, and more specifically, the present invention is directed to an improved process for the preparation of squaraine compositions from the half esters of squaric acid. In one embodiment, the present invention involves the preparation of certain squaraine compositions by the reaction of an alkyl squarate with aniline derivatives. The squaraine compositions resulting from this process are useful for incorporation into layered photoresponsive imaging devices wherein, for example, the sensitivity thereof can be varied or enhanced, enabling these devices to be capable of being responsive to visible light, and infrared illumination needed for laser printing, especially with gallium arsenide diode lasers. Accordingly, there is envisioned photoresponsive devices containing the squaraine compositions prepared in accordance with the present invention, situated between a photogenerating layer and a hole transport layer, or situated between a photogenerating layer and a supporting substrate of the device.
Photoconductive imaging members containing certain squaraine compositions, particularly hydroxy squaraines, are known. Also known are layered photoresponsive devices with photogenerating layers and transport layers, reference U.S. Pat. No. 4,265,990. Examples of photogenerating layers disclosed in this patent include trigonal selenium, and phthalocyanines, while examples of transport layers that may be selected are comprised of certain diamine dispersed in an inactive resinous binder composition. Moreover, the use of certain squaraine pigments in photoresponsive imaging devices is disclosed in a copending application, wherein there is described an improved photoresponsive device containing a substrate, a hole blocking layer, an optional adhesive interface layer, an inorganic photogenerating layer, a photoconductive composition capable of enhancing or reducing the intrinsic properties of the photogenerating layer, and a hole transport layer. As photoconductive compositions for this device, there can be selected various squaraine pigments, including hydroxy squaraine compositions of the formula as outlined on page 13, beginning at line 21 of the copending application, U.S. Ser. No. 414,997, the disclosure of which is totally incorporated herein by reference, entitled Multilayered Photoresponsive Device for Electrophotography. Additionally, there is disclosed in U.S. Pat. No. 3,824,099 certain photosensitive hydroxy squaraine compositions. According to the disclosure of this patent, the squaraine compositions are photosensitive in normal electrostatographic imaging systems.
In another copending application, there is described novel squaraine compositions of matter, such as bis-9-(8-hydroxyjulolidinyl)squaraine, and the use of these compositions as imaging members. One of the imaging members disclosed contains a supporting substrate, a hole blocking layer, an optional adhesive interface layer, an inorganic photogenerating layer, a photoconducting composition layer capable of enhancing or reducing the intrinsic properties of the photogenerating layer, which compositions are comprised of the novel julolidinyl squaraines materials illustrated in the copending application, and a hole transport layer.
Processes for preparing squaraine compositions generally involve the reaction of squaric acid with an amine. Thus, for example, the novel julolidinyl squaraine compositions disclosed in the referenced copending application are prepared by the reaction of an aromatic amine and squaric acid, in a molar ratio of from about 1.5:1 to 3:1 in the presence of a mixture of an aliphatic alcohol and an optional azeotropic cosolvent. About 200 milliliters of alcohol per 0.1 mole of squaric acid are used, while from about 40 milliliters to about 4,000 milliliters of azeotropic material are selected. The squaric acid reaction is generally accomplished at a temperature of from about 50 degrees Centigrade to about 130 degrees Centigrade. Illustrative examples of amine reactants include 8-hydroxyjulolidine, while examples of aliphatic alcohol selected include 1-butanol, with the azeotropic materials being aromatic compositions such as benzene and toluene. Moreover, there is disclosed in a copending application, U.S. Ser. No. 557,796/83, entitled Synthesis of Photoconductive Squaraines, the disclosure of which is totally incorporated herein by reference, processes for preparing squaraine compositions by the reaction of a dialkyl squarate and an aromatic aniline. More specifically, there is disclosed in this copending application an improved process for the preparation of squaraine compositions which comprises reacting a dialkyl squarate, with an aniline, in the presence of an acid catalyst and an aliphatic alcohol, at a temperature of from about 60 degrees Centigrade to about 160 degrees Centigrade.
While the above processes for preparing squaraine compositions may be suitable for their intended purposes, there continues to be a need for other processes wherein squaraine compositions, useful as photoconductive materials, can be prepared. Additionally, there remains a need for simple, economical processes for preparing squaraine compositions wherein the squaraine products obtained contain substantially less impurities than those squaraines resulting from the squaric acid process, as it is believed that the presence of impurities in the squaraine compositions resulting from the squaric acid process causes the photosensitivity of these compositions to vary significantly, and in many instances, to be lower than the squaraine compositions prepared in accordance with the process of the present invention. Further, there continues to be a need for novel squaraine compositions which, when selected for layered photoresponsive imaging devices, allow the generation of acceptable images, and wherein such devices can be repeatedly used in a number of imaging cycles without deterioration thereof from the machine environment or surrounding conditions. Moreover, there remains a need for processes for preparing certain squaraine compositions, wherein the resulting products when incorporated into imaging members exhibit excellent dark decay and superior photosensitivity. Also, there is provided in accordance with the process of the present invention xerographic photoconductive devices comprised of the infrared sensitive squaraine photogenerating materials prepared in accordance with the process of the present invention and possessing desirable sensitivity, low dark decay, and high charge acceptance values.